Converters with electrical isolation are used for the galvanically decoupled transfer of electrical energy from an input side to an output side. Such converters are used in various applications for current or voltage supply, such as, for example, in clocked switched-mode power supplies. In the case of clocked converters, controllable switches which can be in the form of power switches are used and operated in clocked fashion in order to transfer electrical energy onto the output side. Galvanically decoupled energy transfer can be achieved by using a transformer or another transfer device. Such galvanic isolation or electrical isolation is required in the case of operating devices for light-emitting means for safety reasons in order to isolate an ELV (“Extra-Low Voltage”) region from regions with a higher supply voltage, in particular mains voltage, by means of a so-called potential barrier or SELV barrier.
Converters which are in the form of so-called resonant converters which have a resonant circuit can be used to operate light-emitting means. The resonant circuit can be a series or parallel resonant circuit. When configuring converters, one aim is to keep losses low. Resonant converters which comprise an LLC resonant circuit having two inductances and one capacitance can be controlled in resonant or quasi-resonant fashion on the primary side. Such converters have the advantage that energy-efficient operation with relatively low switching losses is possible.
Converters for light-emitting means or operating devices which comprise such converters can be configured or operated as a constant current source (also referred to as FCC or “Fixed Constant Current” device) or a constant voltage source (also referred to as FCV or “Fixed Constant Voltage” device). Constant voltage sources can be used, for example, for LED modules which have electronics in order to ensure a corresponding power supply to the LEDs with a predetermined current from the output voltage provided by the constant voltage source.
When the constant voltage source for operating LEDs is manufactured, the number of LEDs for which the corresponding converter is intended to be used is generally not yet known. If the converter is optimized for a specific number or type of LEDs or a specific LED module, a corresponding indication can be provided to the user of the converter for said converter only to be used given the respective type of LEDs or the corresponding LED module. However, it is not ensured that the user will stick to this instruction. It is therefore desirable to specify converters which can automatically identify a load connected to the output of the converter. This makes it possible to adapt the operation of the converter to the load, if necessary.
One approach for load identification consists in a measurement which is performed at the output or at another suitable point in the secondary side of the converter. The voltage detected on the secondary side can then be fed back to the primary side via an insulator. Bypassing of the SELV barrier requires corresponding components which increase the installation space and/or costs of the operating device. US 2012/0033453 A1 describes an example of a resonant converter which comprises a half-bridge and an LLC circuit and in which an insulator is provided in order to feed back a variable measured on the output side to the input side. US 2012/0033453 A1 also describes an example of a resonant converter in which switches in the secondary side of the converter are controlled. This requires corresponding circuit components, in particular power switches, on the secondary side. It would be desirable to realize load identification which enables adaptation of the operation of the converter to the identified load in a simple manner. In particular, it would be desirable to realize load identification and adaptation of the operation of the converter to the identified load without a measurement needing to be carried out on the secondary side for this purpose.
There is a demand for apparatuses and methods which offer improvements in respect of the mentioned aims. In particular, there is a need for apparatuses and methods in which the complexity in terms of circuitry and/or the costs which are associated with conventional apparatuses for bypassing the SELV barrier can be reduced or avoided. There is also a need for such apparatuses and methods which enable efficient energy transfer.